Alminum alloy energy-absorbing member

ABSTRACT

An aluminum alloy energy-absorbing member, which satisfies the conditions of α≧24 and (α×σ)≧6000, wherein α (%) is the rupture elongation at a gauge distance of 5 mm, and σ (MPa) is a 0.2% proof stress value, in the extruding direction of an aluminum alloy extruded material. This is an aluminum alloy energy-absorbing member that is lightweight, high in energy absorption, adequate in required mechanical strength, and preferable as an impact-absorbing member for an automobile, and the like.

FIELD OF THE INVENTION

[0001] The present invention relates to an energy-absorbing membercomposed of an aluminum alloy extruded material. More particularly, theinvention relates to an energy-absorbing member preferably used as aframe material for a car body side member, for reducing the impacteffect on passengers in the event of a collision of a transport vehicle,especially an automobile.

BACKGROUND OF THE INVENTION

[0002] In transport vehicles such as automobiles, recently, protectionof passengers from collision impact is becoming more and more important,and in automobiles, in particular, it will become obligatory to equipthem with structure and devices for protecting passengers in the eventof a crash. Specifically, in the front engine section and rear trunksection of an automobile, structure and means are being devised forabsorbing crash energy by accordion-like plastic deformation ofstructural members, such as side members, at the time of a collision. Asthe structural members for absorbing such crash energy, hitherto,cold-rolled steel sheets have been used, and they are assembled by pressforming or spread welding.

[0003] Lately, however, from the viewpoint of environmental problems andautomotive performance improvement, lightweight vehicles are demanded,and aluminum materials, which are lighter than steel sheets, are beingstudied to apply. As the aluminum material conforming to this purpose,an extruded material is being highly expected, because a structuralmember of complicated shape can be easily manufactured, and vehicleweight can be more reduced than sheet materials.

[0004] Necessary material characteristics in such an energy-absorbingmember include (1) fitness for hollow extrusion, (2) adequate mechanicalstrength as a structural member, (3) large energy absorption upon acollision, and (4) fitness for welding.

[0005] As an energy-absorbing member made of aluminum alloy, materialshaving rupture elongation and local (locally-caused) elongation definedin a specified range, are proposed in JP-A-7-118782 (“JP-A” meansunexamined published Japanese patent application), but the energyabsorption, which is the most important characteristic for anenergy-absorbing member, was not sufficient.

[0006] Among conventional aluminum alloy extruded materials, Al—Mg—Sialloy and Al—Zn—Mg alloy are known to be relatively excellent inmechanical strength and elongation, but there is the problem that theirenergy absorption is insufficient by only conventional extrusion.

SUMMARY OF THE INVENTION

[0007] The present invention is an aluminum alloy energy-absorbingmember, which satisfies the conditions of α≧24 and (α×σ)≧6000, wherein α(%) is the rupture elongation at a gauge distance of 5 mm, and σ (MPa)is a 0.2% proof stress value, in the extruding direction of an aluminumalloy extruded material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is an explanatory view showing a method of the compressiontest in the examples.

[0009]FIG. 2 is an example diagram of measurement of a displacement loadcurve of the compression test in the examples.

DETAILED DESCRIPTION OF THE INVENTION

[0010] The present inventors intensively investigated theenergy-absorbing properties and material characteristics of aluminumalloy extruded material, and discovered that the energy absorptioncannot be evaluated correctly by the combination of rupture elongationand local elongation of conventional tensile test specimens of JIS No.13B and JIS No. 5, and that the energy absorption depends on acorrelative relation between the rupture elongation at a gauge distanceof 5 mm and a 0.2% proof stress value. The present invention has beenaccomplished based on these findings.

[0011] That is, according to the present invention there is provided: analuminum alloy energy-absorbing member, satisfying the conditions ofα≧24 and (α×σ)≧6000, wherein α (%) is the rupture elongation at a gaugedistance of 5 mm, and σ (MPa) is a 0.2% proof stress value, in theextruding direction of an aluminum alloy extruded material.

[0012] The values of α and σ in the present invention are valuesobtained by tensile testing at a tensile speed of 5 mm/min, using JISNo. 13B test specimens. The rupture elongation α at a gauge distance of5 mm in the extruding direction is the value (%) expressing the rate ofelongation to the initial length of 5 mm, by performing the tensile testby drawing lines at intervals of 5 mm in the vertical direction to theextruding direction in the parallel section of the specimen, andmeasuring the interval of the lines when the specimen is ruptured.

[0013] The energy-absorbing member of the present invention is made ofan aluminum alloy extruded material. As long as the values of α and σare as described later, the composition of the aluminum alloy is notrestricted, but an Al—Mg—Si alloy or an Al—Zn—Mg alloy can be preferablyused, because the mechanical strength and elongation are relativelyhigh.

[0014] The aluminum alloy extruded material used in the energy-absorbingmember of the present invention has the following values as the ruptureelongation α (%) of a gauge length of 5 mm and a 0.2% proof stress valueσ (MPa), in the extruding direction.

[0015] The value of α of the aluminum alloy extruded material used inthe present invention is 24% or more, preferably 30% or more. If thevalue of α is too small, the member is not deformed uniformly,accordion-like, when receiving an impact, and the intended energyabsorption property is not obtained. The upper limit of α is generally60% or less.

[0016] The product of α and σ (α×σ) of the aluminum alloy extrudedmaterial is 6000 or more, preferably 6500 or more. If the value of (α×σ)is too small, the energy absorption in plastic deformation of materialis small, and it cannot be used as an energy-absorbing member. The upperlimit of (α×σ) is generally 100000 or less.

[0017] The energy absorption property of the energy-absorbing member ofthe present invention is an energy-absorbing amount in compressiontesting of generally 10 kg·m or more, preferably 12 kg·m or more.

[0018] If necessary, by adjusting the composition of the aluminum alloy,or adjusting the heat treatment condition, the aluminum alloy extrudedmaterial having such values of α and σ can be obtained. The method ofadjustment varies with the composition of the alloy to be used, and ifthe value of α is too small, for example, it is adjusted by heattreatment. If the value of (α×σ) is too small, it may be adjusted byadding an element for increasing the mechanical strength, or by changingthe aging condition.

[0019] By using the aluminum alloy extruded material adjusted to suchvalues of α and σ, an energy-absorbing material that prevents a decreaseof the energy-absorbing amount while maintaining the necessarycharacteristics such as mechanical strength, can be obtained.

[0020] The shape and size of the energy-absorbing member of the presentinvention are not particularly restricted, and it may be properly usedas a member necessary for absorbing energy, for example, at a crash.Specifically, in an automobile, for example, it is preferably used as amember for lessening the impact effect on passengers in the event of acollision. It may be used as a frame material for a side member, and abumper beam material, and the like.

[0021] The energy-absorbing member of the present invention is made of alightweight aluminum alloy, and it has high energy absorption whilesatisfying the necessary mechanical strength and the like as astructural member. Therefore, the present invention is very useful as animpact-absorbing member for an automobile and the like.

[0022] The present invention is described in more detail based on thefollowing examples and comparative examples, but the invention is notlimited to those.

EXAMPLES Examples 1 to 9, Comparative Examples 1 to 4

[0023] Each of alloys having the composition shown in Table 1 was meltedand casted into a billet of 220 mm in diameter, then the billet washomogenized for 2 to 8 hours at 470 to 580° C., and extruded into asquare form with a cross inside, with one side of 100 mm and a wallthickness of 2.5 mm. Further, as shown in Table 2, the thus-obtainedextruded material was fan-cooled right after extrusion, and aged, toobtain a T5 tempered material (which is referred to as “air-cooled” inTable 2), or the material was held at a temperature of 470 to 520° C.for 40 minutes, cooled in water, and aged, to obtain a T6 temperedmaterial (which is referred to as “water-cooled” in Table 2), and thefollowing tests were conducted.

(1) Tensile Test

[0024] Each of the materials was cut into a JIS No. 13B test specimen,lines were drawn at intervals of 5 mm in the vertical direction to theextruding direction in the parallel section of the specimen, and thetest was conducted at a tensile speed of 5 mm/min.

[0025] The elongation α (%) after rupture in the parallel section of 5mm, the 0.2% proof stress value σ (MPa), and the tensile strength (MPa)were measured, and the results are shown in Table 2.

[0026] Tensile strength of 150 MPa or more is sufficient for use as astructural member of an automobile.

[0027] Separately, each of the materials was cut into a JIS No. 13B testspecimen, and the tensile test was conducted in the same manner as inthe above, except that the gauge length was changed to 50 mm-interval,and the overall elongation (ε (%)) of each specimen was measured.

[0028] The results are also shown in Table 2.

(2) Compression Test

[0029] As shown in FIG. 1, a shaped specimen of 300 mm in length wasloaded at a compressive speed of 10 mm/min, and the energy-absorbingamount was determined from the load, which was applied from the start ofcompression until compressive deformation of 100 mm, and the amount ofdeformation. An example of measurement of a displacement load curve inthe compression test is given in FIG. 2. The obtained energy-absorbingamount is shown in Table 2. TABLE 1 Alloy Composition (wt %) (balanceAl) No. Si Fe Cu Mn Mg Cr Zn Zr Ti Remarks 1 0.48 0.17 — — 0.5  — — —0.02 JIS 6063 2 0.35 0.19 — — 0.48 — — — 0.02 JIS 6063 3 0.51 0.18 0.090.08 0.6  0.02 — 0.03 0.01 JIS 6N01 4 0.7  0.22 0.08 0.09 0.72 0.02 0.010.03 0.02 JIS 6N01 5 0.71 0.23 0.25 0.06 1.11 0.23 — — 0.01 JIS 6061 60.09 0.22 0.08 0.12 0.73 0.02 5.54 0.18 0.02 JIS 7003 7 0.1  0.23 0.090.42 1.37 0.01 4.48 0.17 0.01 JIS 7N01 8 0.88 0.17 0.53 0.11 0.72 0.08 —— 0.03 —

[0030] TABLE 2 Aging condition Tensile Energy Alloy HardeningTemperature Time α σ ε strength absorption No. No. condition ° C. hr %MPa α × σ % ε × σ MPa kg · m Example 1 1 Air-cooled 200  2 42 198 831616.6 3287 230 13.9 Example 2 2 Air-cooled 180 10 34 196 6664 13.2 2587217 13.4 Example 3 3 Air-cooled 190  1 36 176 6336 15.8 2781 236 12.4Example 4 3 Water-cooled 160  8 28 244 6832 12.2 2977 269 16.2 Example 54 Air-cooled 180  6 26 249 6474 14.4 3586 277 16.5 Example 6 6Air-cooled 150 12 36 262 9432 17   4454 314 16.6 Example 7 7 Air-cooled120 24 30 315 9450 17   5355 357 17.2 Example 8 5 Water-cooled — — 52147 7644 18.2 2675 238 12.3 Example 9 3 Air-cooled — — 48 134 6432 16.82251 225 12.2 Comparative 5 Water-cooled 170 10 20 329 6580 10   3290341  7   Example 1 Comparative 4 Air-cooled 210  6 28 203 5684 13.4 2720244  8.4 Example 2 Comparative 7 Air-cooled — — 22 241 5302 18.2 4386361  9.3 Example 3 Comparative 8 Air cooled — — 34 147 4998 13.6 1999268  9.8 Example 4

[0031] As is apparent from Table 2, in Examples 1 to 9 according to thepresent invention, a quite large energy-absorbing amount was obtainedwhile maintaining the necessary material strength. Contrary to theabove, sufficient energy absorption was not obtained in ComparativeExamples 1 to 4, in which α<24% and/or (α×σ)<6000.

[0032] When the rupture elongation (α) and the value (α×σ) were withinthe range defined in the present invention, an excellentenergy-absorbing characteristics were obtained.

[0033] By contrast, if evaluated by the overall elongation (ε) insteadof the rupture elongation (α), it is understood that no correlativerelation was recognized at all between the magnitude of energyabsorption and overall elongation (ε) or (ε×σ). That is, the ruptureelongation (α) and overall elongation (ε) have different meanings asphysical properties (value), and the overall elongation (ε) cannot beused instead of the rupture elongation (α) as a parameter of theenergy-absorbing characteristic. More specifically, different from therupture elongation (ε) of the very narrow gauge length of 5 mm definedin the present invention, the overall elongation (α) at the gauge lengthof 50 mm employed conventionally in the evaluation could not be used asa means for defining or evaluating the energy-absorbing characteristic,or for defining or evaluating the material excellent in compression(crushing) buckling resistance as an automotive structural member.

[0034] Having described our invention as related to the presentembodiments, it is our intention that the invention not be limited byany of the details of the description, unless otherwise specified, butrather be construed broadly within its spirit and scope as set out inthe accompanying claims.

What is claimed is:
 1. An aluminum alloy energy-absorbing member,satisfying the conditions of α≧24 and (α×σ)≧6000, wherein α (%) is therupture elongation at a gauge distance of 5 mm, and σ (MPa) is a 0.2%proof stress value, in the extruding direction of an aluminum alloyextruded material.
 2. The aluminum alloy energy-absorbing member asclaimed in claim 1 , wherein the aluminum alloy is an Al—Mg—Si alloy oran Al—Zn—Mg alloy.
 3. The aluminum alloy energy-absorbing member asclaimed in claim 1 , which is used as a frame material for a sidemember, or a bumper beam material.